Though many drugs are widely used both legally and illegally, comparatively little is known about the ways in which development and loss of tolerance may differ for different classes of these drugs, or about ways in which behavioral factors themselves may influence the time course and extent of tolerance development (behavioral tolerance). This project will attempt to more fully characterize the importance of behavior itself in the development of tolerance and cross-tolerance to a variety of classes commonly abused drugs (psychomotor stimulants, barbiturates, minor tranquillizers, narcotics, and cannabinoids). The project will focus on schedule-controlled behavior that is maintained by food presentation, shock avoidance, and shock titration, and is suppressed by noxious events (punishment). This project is developed specifically to study the influences on tolerance of: 1. "Response Cost" - Experiments will determine the importance and generality of the influence on tolerance development by drug-produced changes in response consequences like reinforcer frequency and reinforcer distribution, and 2. "Associative Effects" - Experiments will determine the general importance on tolerance development of those specific environmental features which are regularly present during the chronic administration of a drug.